
Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-145
SERIAL
I/F
COMMUNICATION
16
PROCESSOR
MODULE
16.7.7 GCI Interface Operation
The normal mode of the general circuit interface (GCI) and SCIT are fully supported by the
MPC823. It also supports the D channel access control in S/T interface terminals by using
the command/indication (C/I) channel for that function.
The GCI bus consists of four lines—two data lines, a clock, and a frame synchronization line.
Usually, an 8kHz frame structure defines the various channels within the 256kbps data rate.
The MPC823 supports an independent GCI bus and has independent receive and transmit
sections. The interface can also be used in a multiplexed frame structure on which up to
eight physical layer devices multiplex their GCI channels. In this mode, the data rate would
be 2,048kbps. In the GCI bus, the clock rate is twice the data rate. The serial interface
divides the input clock by two to produce the data clock. The MPC823 also has data strobe
lines that are used as an interface for devices that do not support the GCI bus. The GCI
signals for each transmit and receive channel are as follows:
L1RSYNCA—Used as a GCI sync signal. Input to the MPC823. This signal indicates
that the clock periods following the pulse designate the GCI frame.
L1RCLKA—Used as a GCI clock. Input to the MPC823. The L1RCLKA signal is twice
the data clock.
L1RXDA—Used as a GCI receive data. Input to the MPC823.
L1TXDA—Used as a GCI transmit data. Open-drain output. Valid only for the bits that
are supported by the IDL. Otherwise, it is three-stated.
In addition to the 144kbps ISDN 2B+D channels, the GCI provides five channels for
maintenance and control functions:
B1 is a 64kbps bearer channel
B2 is a 64kbps bearer channel
M is a 64kbps monitor (M) channel
D is a 16kbps signaling channel
C/I is a 48kbps C/I channel (includes Tand E bits)
Figure 16-59. GCI Bus Signals
B1
B2
MONITOR
C/ I
D1 D2
T
E
B1
B2
MONITOR
C/ I
D1 D2
T
E
L1SYNC
L1RXD
L1CLK
L1TXD
(CLOCK IS NOT TO SCALE)
(2X THE DATA RATE)